1. Field of the Invention
The present invention relates to an IP telephone system, an IP telephone apparatus and a communications method that perform voice communication via an IP network.
2. Description of Related Art
The recent rapid growth of the Internet has drawn attention to an IP telephone system that enables low-cost voice communications with telephone apparatuses at remote places as well as free voice communications between IP telephone apparatuses owned by subscribers. However, dishonest telemarketing agencies have been taking advantage of IP telephone systems using such low-cost or free communication services, causing a social problem.
Such unsolicited telemarketing calls may be blocked by using a caller identification function. For example, one possible countermeasure is to display, at a destination telephone apparatus, a telephone number of a source telephone apparatus, the telephone number of a source telephone apparatus being specified in header “From” in the “INVITE” message transmitted according to the SIP protocol. The SIP is a common call control protocol utilized in the IP telephone systems. This method allows users to screen out telephone calls from unidentified callers.
On the other hand, as an underlying technology, ENUM is emerging as the focus of attention. ENUM enables communications according to users' individual circumstances by effectively managing information used for diverse communications tools, including telephones, facsimiles, cellular phones and electronic mail. ENUM is designed to identify the Internet service with a unique global identification number such as the E.164 number, using the DNS (Domain Name System). Currently, the IETF (Internet Engineering Task force) is seeking to standardize ENUM platforms, where protocol specifications are discussed (See Publication 1, for example).    [Publication 1] Issued by ENUM Trial Japan “ENUM Trial Japan First Report” May, 2004
When using the above-described measure, however, it is necessary to ignore all calls from unidentified callers in order to avoid telemarketing calls. This results in a situation where communication cannot be established with any party who has called for the first time. As a result, a situation occurs where no communication can be established with parties that needed to be contacted, thus leading to the problem of no communication being allowed through such a telephone system.